The aim of this proposal is to study the characteristics of resistance arteries, and their adrenergic innervation. Relatively little is known from direct in vitro experimentation of this important class of vessels. They will be obtained from the vasculature of the ear of the rabbit and compared with the central ear artery which has been extremely well characterized. Utilizing a resistance vessel myograph that allows study of arteries as small as 50 Mu O.D. and structural and biochemical measurements, functional features of their innervation, smooth muscle, and endothelium will be documented. These will be related to vessel diameter and the in vivo intramural pressure they experience. The objectives of research include an assessment of the asymmetry of the response of the artery wall to agonists entering through its outer and inner surface which is dependent upon cellular uptake systems and possibly long-term neurotropism, differences in Alpha- and Beta-adrenoceptorlocation, intimal dependent dilation, myogenic tone, functional consequences dependent upon differences in synaptic cleft width and agonist sensitivity in relation to resting length. The overall objective is to understand changes that occur in vessel characteristics with change in their diameter. Although resistance arteries play a pivotal role in circulatory function and appear to be altered in hypertension, only recently have direct studies of these vessels been undertaken in vitro.